The present invention relates to a display unit using organic electroluminescence devices (hereinafter, referred to often as “organic EL devices”).
Recently, in studies and developments for display units coping with the tendency toward higher speed of information, there have been demands toward enlargement of display units such as televisions and monitors not only for use in public locations (railroad stations, buildings, and antechambers and business rooms of hotels) but also for use in general households.
If the screens of display units are enlarged, however, CRTs (Cathode-Ray Tubes) or monitors such as liquid crystal projectors cause a problem that since the weight and size become large with the increased screen size, the handling becomes inconvenient and the occupied area becomes large.
For this reason, flat display units being thin and lightweight have been required. A display unit using organic EL devices excellent in high efficiency, thinning, lightweightness, and low dependency on viewing angle has become a focus as one of these flat display units, and has been actively studied and developed.
Display units using organic EL devices are now being applied to small-sized display units such as digital cameras and cellular telephones. On the other hand, such display units have been regarded as difficult to be applied to medium/large-sized display units such as monitors for personal computers and televisions and large-sized display units for home theaters. For example, as the size of a substrate of such a display unit using organic EL devices becomes large, the equipment scale becomes large to thereby raise the production cost, and it becomes difficult to uniformly form an organic EL film on the large screen and to obtain uniform brightness over the large screen.
If a panel is of an active matrix type, one or more TFTs (Thin Film Transistors) are provided in pixels for driving the organic EL devices. In this case, as the screen size of the panel becomes larger, the production yield of the TFTs becomes lower due to pixel failures or the like, and thereby it fails to ensure high productivity. Also, if a p-channel transistor is required to be provided in each pixel, or if a CMOS (Complementary Metal Oxide Semiconductor) circuit is formed around a screen for driving the pixel, low-temperature polycrystalline TFTs must be provided. In this case, it is difficult to form the polycrystalline TFTs at once on a large screen by polycrystallization of amorphous silicon by irradiation with laser beams such as excimer laser beams because of the limitation of the width of the laser beams used for polycrystallization. In the case of repeating the laser irradiation by a plurality of times, it is difficult to keep the equalization of TFT characteristics at a joint between laser beams, with a result that portions corresponding to the joints between laser beams form a stripe pattern.
To solve such a problem, in the field of display units using organic EL devices, there has been known a technique of forming one large screen by joining a plurality of small-sized panels to each other on the same plane, as disclosed in Japanese Patent Laid-open Nos. Hei 5-205875, 2001-22293, 2001-100668, 2002-6779, and 2002-108253.
With respect to such a technique, although it is required to make a distance between pixels as small as possible for realizing high-definition of a display screen, it is generally difficult to form patterns of pixel circuits, wiring lines, pixel electrodes in such a manner that the patterns extend to an end face of a substrate of each panel. Accordingly, a large display screen is actually produced by forming patterns of pixel circuits, wiring lines, and pixel electrodes on a raw substrate larger than a finish substrate of a small-sized panel forming part of the large screen, highly accurately cutting the raw substrate at the vicinity of an end face (which is taken as a joint face) by a substrate cutter such as a laser cutter or a dicer, and joining the panels thus obtained to each other.
By the way, in the case of producing one display screen (large screen) by joining a plurality of panels to each other as described above, at a joint portion between adjacent two of the panels, it is required to make a distance between the outermost pixels on both the panels as small as possible in order to make the joint portion inconspicuous. Accordingly, a distance from a cut end face of each panel to an end of the outermost one of pixels on the panel becomes very short. This may cause an inconvenience. In particular, if organic EL devices are formed by low-molecular EL devices, a film of the EL devices, which is formed by a vacuum vapor-deposition process using an opening mask, becomes larger than the opening, to be thereby close to or in contact with the cutting end face. In this case, when panels are joined to each other, the end of the outermost organic EL device is exposed at a joint portion between the adjacent two of the panels. As a result, there occurs a problem associated with erosion of the organic EL devices by permeation of moisture, air, and the like from the exposed portion of the outermost organic EL device.